As is well known, wind turbines are devices capable of generating electrical energy from air currents. In order to operate, these wind turbines are mounted on top of a wind tower, which comprises a foundation, a tubular shaft and wind turbine itself.
The shaft of a wind tower usually has a height between 60 and 120 metres, and is built from heavy materials heavy such as steel and/or reinforced concrete. Likewise, the wind turbine of a wind tower is provided with very large blades, usually between 20 and 60 metres long, and parts such as the rotor and the outer cover, often called a nacelle, which have important mass.
For all the above, the total weight of a wind tower is very high, usually hundreds of tonnes.
Moreover, in view of the height of the wind towers, their shaft is usually produced in segments, usually subdivided in turn into voussoir-like parts that are transported individually to the location of use and once there are mounted in their final use position to form the shaft assembly. During the assembly process, regardless of whether it includes or not any pre-assembly stage of voussoirs for each segment, it is common to coaxially assemble tubular shaft segments. As a result, it is common for wind towers to include, between the tubular segments forming such towers, horizontal joints that are subjected to extremely high loads.
The cost associated to structures of such magnitude is, as you can imagine, very high.
Solutions for horizontal joints have therefore been proposed, often as part of global construction solutions for wind towers, in order to approach these loads economically. One of such horizontal joint solutions includes the use of cable anchoring means that include at least one tongue and grooved device for cable anchoring. With regard to this, see for example document EP 2253782 A1, especially FIG. 3, which shows a tongue and groove device for cable anchoring in a joint between tubular segments of a wind tower shaft. Basically, with specific reference to said FIG. 3 of document EP 2253782 A1 as an illustration, a tongue and grooved anchoring device is provided on respective opposite edges of a voussoir (2 bottom) of a first tubular segment (2, 3 bottom) and a voussoir (2 top) of a second tubular segment (2, 3 top) of a tower shaft (1), and includes: a cable (4a), that has a portion that is embedded in a fixed manner inside the first tubular segment and a portion that protrudes from the first tubular segment towards the second tubular segment; a through duct (24) on the second tubular segment, intended to receive the protruding portion of the cable; and fastening means (22) to fasten the cable in its position, apparently formed in this case by a screw or wedge device that is applied to the free end of the protruding portion of the cable once it has been passed through the through hole, as is known in the art.
However, the horizontal joints that use tongue and grooved devices for cable anchoring exhibit certain drawbacks, associated mainly to the assembly procedure, as described below.
A tubular segment is usually mounted using a descending movement, for a coaxial approximation of such tubular segment to a tubular segment that has already been placed, until the bottom edge of said tubular segment to be mounted rests either directly or using some kind of mortar on the top edge of the tubular segment that has already been placed. The cable must be threaded simultaneously with this approximation, that is, the free end of the protruding portion of the cable for a segment must be made to coincide vertically with the opening of the corresponding receiving duct in the other segment and said free end must be kept in that position as long as necessary during the descending movement of the segment to be mounted so that said free end passes through said opening and is housed in said receiving duct. But usually the axial development of the protruding portion of the cable is not straight and predetermined when starting the assembly process, but rather it has a natural shape of an axial development such that the free end of the protruding portion is not centred with respect to the opening of the corresponding receiving duct. The most simple cause is that the cable is provided on spools, which favours that the cable tends to wind itself up after installation. In particular, in cases in which the protruding portion extends upwards, the protruding portion is usually of such a length that in these cases said protruding portion flexes due to its own weight, even in the cable emerges in an entirely vertical manner. In any case, the protruding portion of the cable may already emerge with a certain inclination (see for example document ES 2407780 A2, FIG. 4) which may cause such mentioned off-centring. This usually means providing means and/or procedures intended for holding the free end of the protruding portion in coincidence with the opening of the corresponding receiving duct during said approximation movement.
Usually, the means and/or procedures intended to hold the free end of the protruding portion of the cable in coincidence with the opening of the corresponding receiving duct during said descending approximation movement include an operator holding the protruding portion of the cable in place. Since most joints include a multiplicity of tongued and grooved anchoring devices and the cables of them all must be simultaneously threaded, the threading operation involves a lot of labour as well as a serious risk to the operator, who must remain placed under a suspended and moving tubular segment during the threading operation, which is even forbidden in some legislations.
This problem is accentuated when there are cables in both directions, as is common (protruding from the both the upper segment and the lower segment), and also the operation must be performed at a certain height, with the corresponding limitations of accessibility and space available for operating when threading, fastening or wedging the cables, and in particular when tightening them, which may involve the use of jacks of considerable weight and size.